An upskirt pervert targeted schoolgirls and women on escalators at supermarkets, shopping centres and train stations.
Daniel Jones secretly filmed eight children, some believed to be as young as 10, in a crime commonly known as "upskirting" .
The amassed more than 400 videos and photos, but accidentally recorded his own face on one of the sick clips.
Police found his iPhone had a "covert camera" app, which allowed it to record or take pictures without the screen being active.
Liverpool Crown Court heard it was likely he used this to film a woman getting changed, by pushing it under a cubicle at a shop.
Jones, of Fairlie Drive, Rainhill , was rumbled after an incident at a Tesco store in St Helens, at around 7pm, on May 9, 2018.
Paul Blasbery, prosecuting, said a woman in "a distressed state" called police and said a man had taken photos up her skirt.
Security guards said he was "messing with his phone" and "clearly trying to do something" while being detained at the store.
Police arrived and viewed CCTV, which showed Jones pointing a phone at a woman, who was bending over looking at clothes.
However, no pictures of the woman were found on his iPhone and when arrested, Jones gave a no comment interview.
Officers seized a laptop, pen drive and tower computer from his home, which experts examined, along with the phone.
Mr Blasbery said: "They found a large amount of photos and videos all of a voyeurism type nature, with the user of the phone filming up the skirts of females whilst at various locations on escalators at superstores, shopping centres and at railway stations."
The court heard there were 409 "upskirting" images in total, of which 85 were videos, on his phone and computers.
There were eight videos of children aged between 10 and 15, which were all Category C images, the least serious category.
Jones was brought back in for interview in December 2018, but again made no comment, despite the overwhelming evidence.
Mr Blasbery said analysis of his computer found he had also visited websites "catering for an interest in voyeurism".
Jones admitted an act outraging public decency, at various locations, between May 9, 2017 and May 10, 2018.
He pleaded guilty to taking eight indecent photographs of children and one count of voyeurism, relating to the fitting room video.
Jones, who has no previous convictions, denied possessing indecent images of children, which was ordered to lie on the file.
Tom Watson, defending, said a "positive" pre-sentence report found Jones was "genuinely remorseful" and accepted responsibility.
He said his client had "attempted to trace the path that led him to where he is today, in terms of beginning by viewing things on the internet".
Mr Watson said: "He's utterly ashamed and his principle concern is for his grandparents with whom he lives because of the inevitable - and I mean no criticism of this because it's quite proper - because of the inevitable reporting of this."
He added: "He's not had the sort of relationship with his parents that he might have hoped for in his younger life, but he does have his grandparents and they certainly don't need this in their lives."
Mr Watson said Jones was "acutely embarrassed and distressed", but accepted his crimes were sexually motivated and wanted help.
He said he was deemed low risk and urged a judge to spare him jail, so he could attend a sex offenders treatment programme.
Mr Watson said: "He was an assistant manager with a well known retail store - he's lost his job because of this."
He added: "He does have a partner, who is standing by him. He's fortunate in that regard that she is standing by him.
"He doesn't want to let these people down in the future."
Judge Denis Watson, QC, said the creation of the eight videos of schoolchildren was a "particularly serious offence".
He told Jones it could be said he was "candid enough to admit sexual motivation" for his crimes "but it was perfectly obvious".
The judge said aggravating features of the case included the covert phone app and the "vast number" of images.
Jailing him for 12 months, he said: "Mr Watson, on your behalf, has submitted there is remorse here.
"The remorse must have come very late after two no comment interviews and no indication [of plea] at the lower court."
Judge Watson told Jones to sign on the Sex Offenders Register and comply with a Sexual Harm Prevention Order for a decade.
